Return_Values

   0                  Indicates success. There are no stopped or
                      exited child processes, the WNOHANG option is
                      specified.
   x                  The process_id of the child process. The
                      status of a child process is available.
   -1                 Indicates an error; errno is set to one of the
                      following values:

                      o  ECHILD - There are no child processes to
                         wait for.

                      o  EINTR - Terminated by receipt of a signal
                         intercepted by the calling process.

                      o  EFAULT - The status_location or resource_
                         usage argument points to a location outside
                         of the address space of the process.

                      o  EINVAL- The value of the options argument
                         is not valid.